Conventionally, (meth)acrylic acid alkyl ester-styrene-acrylonitrile copolymer resin polymerized using (meth)acrylic acid alkyl ester monomer, acrylonitrile monomer and styrene monomer can have an excellent balance of appearance and physical properties. This can be attributed to the excellent stiffness and transmittance of (meth)acrylic acid alkyl ester and excellent processability and chemical resistance of acrylonitrile. However, (meth)acrylic acid alkyl ester-styrene-acrylonitrile copolymer resins typically have a high amount of (meth)acrylic alkyl ester and thus can have poor flowability and can be difficult to compound with transparent acrylonitrile-butadiene-styrene (ABS) resins.
(Meth)acrylic acid alkyl ester-styrene-acrylonitrile copolymer resins can be prepared by emulsion, suspension, or bulk polymerization. In emulsion polymerization, the surfaces which can polymerize are widely distributed because the sizes are smaller than surfaces in other polymerization processes and regions can occur in the polymerization with a micelle structure of hundreds to thousands Å. It can also be easy to control temperatures, and polymerization can be stable and can be conducted over a short time. However, emulsion polymerization can result in coloring problems due to the presence of residual polymerization additives and steam discoloration problems. There can also be production efficiency and facilities problems associated with emulsion polymerization because polymer slurries prepared by solidifying the polymer have to be cleaned, dehydrated, and dried. There can also be waste water treatment problems, and the resultant products can exhibit reduced transparency due to extrusion and injection impurities and extruded sheets can have a poor appearance.